//此模块用于文件类型与Content-type的转化
exports.format = {  
    "html" : "text/html",  
    "css"  : "text/css",  
    "js"   : "text/javascript",  
    "json" : "application/json",  
    "ico"  : "image/x-icon",  
    "gif"  : "image/gif",  
    "jpeg" : "image/jpeg",  
    "jpg"  : "image/jpeg",  
    "png"  : "image/png",  
    "pdf"  : "application/pdf",  
    "svg"  : "image/svg+xml",  
    "swf"  : "application/x-shockwave-flash",  
    "tiff" : "image/tiff",  
    "txt"  : "text/plain",  
    "wav"  : "audio/x-wav",  
    "wma"  : "audio/x-ms-wma",  
    "wmv"  : "video/x-ms-wmv",  
    "xml"  : "text/xml"  
};  